Hi Jennifer!
Both parks are a lot of fun. If you can't decide, I recommend going to Disney's Hollywood Studios in the morning and then park hopping over to Epcot in the afternoon. At the Studios, favorite attractions are:
- Rock 'n' Roller Coaster Starring Aerosmith
- Star Tours the Adventures Continues
- The Tower of Terror
- Toy Story Midway Mania
Rock 'n' Roller Coaster and the Tower of Terror are thrill rides and may not be appropriate, especially for your youngest child, but everybody will enjoy Toy Story Midway Mania and Star Tours isn't rough at all!
At Epcot, I recommend concentrating on the Future World portion of the park as most young children don't enjoy the World Showcase part, in my opinion. You can easily spend a whole day in Future World and in fact, for many years, it was my oldest son's favorite theme park.
I hope this helps! Write back if you have any more questions!